1. Field
This application relates to a radio frequency (RF) coil device capable of spatial position adjustment of RF coil elements, a magnetic resonance apparatus employing the RF coil device, and a method of operating the RF coil device.
2. Description of Related Art
Magnetic resonance imaging (MRI) apparatuses, magnetic resonance spectroscopy (MRS) apparatuses, and other magnetic resonance apparatuses are well known as magnetic resonance apparatuses that use a nuclear magnetic resonance (NMR) phenomenon.
MRI apparatuses scan a cross-section of a human body using an NMR phenomenon. Since atomic nuclei, such as hydrogen (1H), phosphorus (31P), sodium (23Na), and carbon isotope (13C), existing in a human body have unique rotating magnetic field constants, according to an NMR phenomenon, an image of the inside of the human body may be obtained by applying electromagnetic waves to the magnetization vectors of the atomic nuclei and receiving a magnetic resonance signal generated by a magnetization vector lying in a vertical plane due to resonance.
A radio frequency (RF) coil is used to apply the electromagnetic waves to the human body to make magnetization vectors within the human body resonate and to receive the magnetic resonance signal generated by the resonance of the magnetization vector lying in the vertical plane. The RF coil is referred to as an RF antenna because it transmits electromagnetic waves to cause magnetization vectors to resonate, and receives a magnetic resonance signal. Making a magnetization vector resonate (i.e., a transmission mode) and receiving a magnetic resonance signal (i.e., a reception mode) may be performed together by a single RF coil (i.e., an RF antenna), or the transmission mode and the reception mode may be performed using two separate RF coils, namely, an RF coil for a transmission mode and an RF coil for a reception mode.
A single RF coil that performs both a transmission mode and a reception mode is referred to as a transceiver coil, an RF coil for transmission only is referred to as a transmission RF coil, and an RF coil for reception only is referred to as a reception RF coil. The transmission RF coil is generally installed on a cylindrical (or oval-cylindrical) frame big enough to receive a human body. However, since the reception RF coil is frequently attached to a human body while in use, it is common to form a head coil, a neck coil, a waist coil, and other coils according to the shapes of parts of a human body on which the reception RF coils are to be used.
MRS apparatuses analyze physical, chemical, and biological features of a material using a magnetic resonance phenomenon. Such MRS apparatuses dispose a target within a magnetic field, induce magnetic resonance by directing a pulse RF signal toward the target via a transmission RF coil, and detect a magnetic resonance signal via a reception RF coil disposed around the target. Since different types of atoms within a target generate different magnetic resonance frequencies, the types of the atoms within the target may be determined by inspecting the spectrum of the magnetic resonance signal received via the reception RF coil.
Much research is being conducted on techniques of acquiring a high-definition, high-quality magnetic resonance image. A technique capable of providing a uniform magnetic field and acquiring a fast, stable, and high-quality image by constructing a transmission RF coil with multiple channels and applying an independent RF signal to each channel is an example of one type of this research. A system that uses a multi-channel RF coil system for transmission due to non-uniformity of a magnetic field occurring within a human body due to a dielectric effect is already commonly used in high magnetic field MRI apparatuses employing a magnetic field strength of 3 Tesla (T) or greater.
Such a multi-channel RF coil needs to be designed to effectively contribute to magnetic field uniformization, called B1 shimming, and to reduce an amount of energy of an electric field that is absorbed by a human body. The amount of energy of the electric field that is absorbed by a human body may be expressed by a specific absorption rate (SAR), which is a rate at which energy is absorbed per mass of tissue. A maximum permissible SAR is strictly regulated by the U.S. Food and Drug Administration (FDA), the International Electrotechnical Commission (IEC), and other regulatory bodies, and this regulation is more strictly applied to medical equipment than to other electronic equipment.
Since a conventional multi-channel transmission radio frequency (RF) coil has a fixed rigid frame structure, a local peak SAR occurs where an RF coil is close to a human body, and cannot be completely removed by B1 shimming. Moreover, if some elements of the RF coil are not used to reduce the local peak SAR, the degree of freedom during B1 shimming is degraded, and thus an expected performance improvement in B1 shimming may not be obtained.